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[OM] Re: OT..but Optical

Subject: [OM] Re: OT..but Optical
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Wed, 18 Jan 2006 18:11:23 -0500
I can't tell you about these two particular models other than offer some 
observations on magnification which you may already know.

The Zeiss Victory is quoted as having better twilight performance 
because is has lower magnification using the same 40mm objective.  The 
exit pupil (objective diameter / magnification) for this 8X binocular is 
5mm which is somewhere near the size of your pupil in twilight and will 
be brighter than the Dialyt which, at 10X has a 4mm exit pupil.

In additon to being brighter in the low light of early morning and late 
afternoon (when birds are active) the 8X glass will be easier to hand 
hold without a monopod or other support.  8X is already about the limit 
for unaided hand holding and I think 10X is getting pretty shaky.  The 
8X glass is also lighter which can make a difference if you're carrying 
them around all day.

Human pupil sizes ranges from about 3mm in full daylight to about 7mm 
when dark adapted at night.  7x50 binoculars are called "night glasses" 
since they have a 7mm exit pupil which is just the right size to fit 
through the dark adapted pupil.  Any of these binoculars, however, waste 
a certain amount of light during the day since the exit pupil is larger 
than can fit into the 3mm pupil of your eye.  For daylight use a 7x50 is 
no brighter than a 7x21 since the emerging light beam from the 7x50 (the 
exit pupil) can't fit into your 3mm eye opening.

I have 8x40 and 7x35 binoculars.  Both are the same relative brightness 
since both have a 5mm exit pupil.  However, I take the 7x35's most of 
the time since they are lighter.

The answer is, of course:  It depends.

Chuck Norcutt

JOHN DUGGAN wrote:
> Hi all,
>       As outdoor types with a passion for good glass I
> am sure I can get good advice on a binocular query I
> have...
> 
> 
>  I have been looking for another pair of good bino's
> for a while, and my favourite photo store is having a
> 20% off sale (what better reason do I need)
>  On offer  Zeiss Dailyt classic rubber armoured 10x40
> T* coated (approx 1980-2) for £250.00 approx $420.00
>      Or    Zeiss Victory 8x40 T* P* phase coated
> optics (approx 2ooo) for £200.00 approx $330.00
>  
> For Zeiss Victory...Nitrogen filled, much newer
> design, lighter, Phase coated optics, better twilight
> performance,closer focus,cheaper.
> For Zeiss Dailyt...Higher mag, A look I have long
> admired.
>  It seems a no brainer...so why am I unsure?
>    Both pairs of bino's are in excellent condition.
>   Any one out there with advice , or experience of
> either pair of binoculars?
> 
> Regards
>   John Duggan,
>      Wales, UK
> 
> 
>               
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